Force measuring apparatus



May 19, 1953 y 4 A; D. MDUFFlE ETAL 2,638,781

FORCE,MEASURING4 APARATUS Filed Oct. 6. 1948 2 Sheets-Sheet 1 En zg;

l M' l (Ittorneg May 19, `1953 A. D. MGDUFFIE Erm.

FOR-CE MEASURING APPARATUS 2 Sheets-Sheet 2 Filed 001:. 6, 1948 PatentedMay 19, 1953 2,633,781 VFORCE MEASURING APPARATUS Archie D. McDue,Berkley, and Warren H. Smith, Detroit, Mich., assgnors to General MotorsCorporation,` Detroit,V Mich., a corpora-I tion of Delaware Applicationcatchers, 194s, serial N6. 53,072

l The present invention relatesto luid means for measuring force and/ortorque. `More particularly it relates to a doublerange fluid forcemeasuring means in which the iiuid pressure is used as an indication ofthe force being measured.

Scales used. to measure dynamometer torques are subject to quite severeforce impulses,` vibra` tion and other adverse operating conditions.Spring scale `have very littledamping action and therefore, theindicator `vibrates greatly making them difficult to read when subjectedto loads having vibratory components. `Beam balance scales, althoughaccurate, require an apprec able amount of time for balancing and arenot suitable for use when continuously varying torques are beingmeasured. Previously used single piston hydraulic scales, in which theforce is determined by measuring the hydraulic pressure, are not subjectto the disadvantages enumerated above, but are quite limited in theirrange of application. These single piston hydraulic scales havesubstantially the saine absolute accuracy throughout the range ofpressures used. For this reason the percentage accuracy-which is ofcourse the most important measure cf accuracy, is very low, whenhydraulic scales suitable for measuring high forces is `used to measurforces of small magnitude. i i It is therefore an object of the presentinvention to produce a fluid force indicating means suitable formeasuring a wide range of force magnitudes.

It is a further object of the present invention to produce a fluid forcemeasuring means suitable for use with a dynamometer. i It is a furtherobject of thepresent invention to produce a dynamometer torque measuringmeans which is highly accurate through a plurality of ranges of torques,and one` which has suitable damping to minimize torque observationerrors.

It is a further object of the present invention to produce a forcemeasuring means which is economical to construct, accurate in indicationand foolproof in operation.

Other objects of this invention will become apparent upon reading thespecification and inspection of the drawings and will be particularlypointed out in the claims.

Referring to the drawings, Figure l is a general arrangement of thepresent invention.

Figure 2 is a cross section `of the hydraulic scales which is part of ithe present invention and` is taken along the line 2,-.-,2 of Figure 3.

r 2 Figure 3 is a horizontal partial sectional view taken along the line3-3 of Figure 2.

Figure 4 is a partial sectional View of the control valves of thehydraulic scales taken along the line 4-4 of Figure 2.

Figure `5 is a phantom view of the control valve and its porting.

Referringmore particularly to Figure 1,` 2 `is an electric motor ofcommercial design which may be energized from kany suitable source ofpower not shown. 4 is a hydraulic pump of suitable commercial designwhich is driven by means of motor 2 and drive shaft 6. If it is `desiredto use a gaseous iiuid insteadof a liquid fluid, as specifically shownin the drawings, this pump 4 could be a blower of suitable design. Thehigh pressure output of the pump 4 is transferred to the hydraulicscales here shown generally as 8 by means of conduit I0. I2 is a returnconduit from the scales 8 to the pump 4. The pistons I4 and I6 of thehydraulic scales 8 are connected tothe torque arm I8 of the dynamometer20 by means of adjustable connecting rod 22. The dynamometer 20 may beof any conventional design and is here schematically shown as anelectrical dynamometer. The torquearm I8 is rigidly secured to thecasing of the dynamometer and is free to receive torque from this casingand rotate a limited amount therewith. The amount of rotation permittedis determined by the position of `the set screws 24 and 26 of themechanical stop member `28. The extension 30 of the torque arm I8 hasattached thereto the piston 32 of the dashpot 34. As will be morespecically described later in the specification, the pistons I4 and I6are urged downwardly by the torque exerted by the arm I8. These pistonsare maintained in position by iiuid pressure introduced against thelower surfaces thereof as will be noted later in the specification. Avalve is provided t0 permit this pressure being introduced to either thepiston I6 or to both the piston I6 and the piston I4. This fluidpressure urges the pistons upwardly `against the force exerted on themby the dynamometer so as `to open ports in the side of their mating cyliinders Where a balance between the fluid pressure and the force isreached. The oil `coming from these ports returns to the sump 46 of thehydraulic scales where it is recirculated by the pump 4. The pressurenecessary tomaintain the pistons in 4equilibrium is measured by notingthe height of the column `in manometer tube 48. It is not necessary touse the same `fluid in the manometer tube as is used'in the fluidscales; for example,`a

gas or liquid may beiused inthe hydraulic scales l ik and its pressuremeasured by means of a column 3 of uid of some other type in themanometer tube. As specifically here illustrated, an oil 50 of lowviscosity may be used in the hydraulic scales and a column 52 of mercuryused in manometer tube. These two liquids are separated by a layer ofwater54. It may thus be readilyseen that the force exerted rby thedynamometer torque arm i8 is balanced by a iiuid pressure, and thisforce is equal to the fluid pressure multiplied by the area the pistonsI4 and IB with their mating cylinders 66 and 63 and the associated oilconduits for operation of the scales. These pistons are mountedcoaxially and held in a proper displaced relationship by means of spacer56. It is quite important in the operation of this device that the axialdisplacement of the pistons have a proper relationship to the distancebetween the ports 'i and 12. These ports permit the exhaust of oilpressure from the pistons. The location of the ports 'I4 is notcritical, these ports being merely overflow ports or bypass ports tobypass the conduits I2. The rod 22 is attached to the piston I4 by meansof a ball and socket joint 'it to permit some angular movement of thearm 22 without causing canting or binding of the pistons i4 and I5 intheir mating cylinders. The plunger or rod 22 is inserted through aclearance opening it to permit this angular movement and a cap iii isattached to 22 to cover this opening thus prevents ing foreign matterfrom getting inte the cylinder 66.

Pressure may be introduced to the lower side of the piston it or tolower side of this piston and also the piston i4 depending upon theposition of the valve fit. Under all positions of this valve, oil underpressure is permitted to enter through the conduit I6, the conduit 82and the port 34 to the lowerside of the piston i6. Under theseconditions the pressure under the piston I6 counteracts all forcesexerted by the plunger or rod 22. As the force exerted by the fluidpressure overcomes the force exerted by the rod 22, the piston It ispushed upwardly until the port lli is opened. When this port is opened,t'he fluid is allowed to escape through this port and the port 86 to thearea above the piston and hence through the conduits 53 and GB back intothe sump 4t. Under such conditions the pressure in the cylinder 63 andhence, in the conduits 82 and B4 is .maintained at a pressure justsufhcient to neutralize the force exerted on the rod E2 and keep thesystem in equilibrium. Under this condition of operation, the pressurein the conduit E4, times the area of the piston I6 is equal to the forceexerted by the plunger 22 plus or minus any zero set made necessary bythe unbalanced weight of the system.

The oil which returns to the sump 4S is iiltered by the iilter 62 andreturned to the pump 4 through the conduit I2 and again put underpressure to operate the system.

Referring now also to Figures 3, 4 and 5, a valving and portingarrangement is shown which permits the simultaneous introduction offluid pressure on both pistons Illl and I. In the valve position shownin the phantom View of Figure 5, pressure is introduced only to thesmaller piston as described above. This valve however may be turned toari-angle of 90 to` another indexed position and maintain this positionby detent and spring arrangement 88. In this new position the conduit 60is closed and the conduit 90 opened. Under these conditions iluid isintroduced to the lower side of the small piston through port 84 asdescribed above, and fluid is also introduced through the conduit S0 andthe port 98 to the lower side of the piston I4. The

v egress of oil through the port 58 and conduit S0 is prevented by theposition of the valve Bil. Under these conditions the pressure underboth pisytons cooperates to oppose the force being exerted by the rod 22and the pistons are moved upwardly until the ports 12 are unmasked bythe piston I4 allowing the oil to escape back through the sump openings94 and the conduit S6. rihe openings of the portion 'I2 relievespressure under the piston I4 and thus permits the system to seek anequilibrium state at a point where the pressure under the pisons i4 andI G times the cross section area of the piston I4 equals the force beingexerted by the rod 22. It may readily be seen that the force under thepiston IG is maintained at all times under this condition of operationto exactly the same pressure as that under the piston i4. This pressureof course is the sume pressure as that now present in the conduit 54.

Operation The system as decribed above is secured to a dynamometer 2l)of conventional design and the dynamometer system placed in operation.Ii the torque to be measured is small, the valve Bil is placed in theposition shown in Figures 4 and 5. If the torque to be measured isgreat, the valve 8@ is displaced 90 to that shown in these `figures soas to align the conduit da with the port mit, and the port im isdisplaced so as to close the conduit fill. With the valve set in eitherof these two positions, depending upon the order of magnitude of thetorque to be measured, the dynamometer is started and the motor 2energized. The operation of the pump 5 by the motor introduces apressure in the line Iii `which is determmed by the back pressure causedto be formed by the force on the arm 22. When the system reaches anequilibrium state as described above, the pressure in the conduit $4 isan exact indication of the force exerted on the rod 22. This pressure isalso exerted by the oil 50 through the water 54 to the mercury 52 in themanometer tube 48. This pressure may be readily determined by observingthe height of the mercury in the tube in the ordinary manner. Undernormal conditions of operation, this manometer has two sets ofgraduations |04 andv 106. One of these 1s calibrated in units of torqueusing the small piston I6 alone, and the other is calibrated in umts oftorque using both pistons. It may thus be readily seen that the torqueexerted by the element 20 is accurately determined by observlng theheight of the mercury in the manometer tube 48 on thhe correctcalibration either I 4 Bi |06 depending upon the position of the valveIt is to be understood also that although the invention has beendescribed with specific reference to a particular embodiment thereof, itis not to beso limited, since changes and alterations therem may be madewhich are within the full intended scope of this invention as defined bythe appended claims. J

We claim: l. A multirange force indicating means including; two pistonsof different diameters coaxially located and axially displaced from eachotherl and having mating cylinders, said pistons rigidly attachedtogether and mechanically secured to a member capable of exerting forceon said piotons, means for selectively introducing luid um der pressureto actuate either the smaller piston, or to actuate both pistonssimultaneously, so as to exert a force in opposition to said iirstmentioned force, and means to measure the pressure of said .fluid andthus determine the magnitude of said first mentioned force.

2. A multirange torque indicating apparatus including; means fortranslating a torque into a force, means for damping the fluctuation ofsaid torque and its resulting force, and means for measuring said force,said last mentioned means as are said pistons, means for introducing aiiuid under pressure selectively to one or both of said pistons, `and amanometer tube to measure the pressure of said fluid and thereb-ydetermine the magnitude of said force.

4. A multirange force measuring apparatus includng: two pistons ofdifferent diameters coaxially located and axially displaced from eachother, means for transmitting an unknown force to be measured to saidpistons, mating cylinders for said pistons, said cylinders havingexhaust ports therein axially spaced the same distance as are saidpistons, means for introducing a uid under .pressure selectively to oneor both of said pistons, said means simultaneously vallowingl withdrawalof the fluid `from one or the other of said exhaust ports, and amanometer tube to measure the pressure of said fluid andy thereforedetermine the magnitude of said force.

5. A multirange force indicating means inoludirig; two positions ofdifilerent diameters rigidly attached together and mechanic-ally sccuredto a member capable of exerting force on said pistons, mating cylindersfor said. pistons having ports therein, means for selectivelyintroducing iluid under pressure to actuate either the smaller piston,or to actuate both pistons simultaneously so as to exert a force inopposition to said inst-mentioned force, said ports being adapted toallow the exhaust of the fluid pressure and thus maintain the pistons ina state of equilibrium, and means to measure the pressure of said fluidand thus determined the magnitude of said rst-mentioned force.

ARCI-IIE D. MCDUFFIE. WARREN H. SNIITH.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,659,736 Zelov Nov. 29, 1927 2,172,095 White Sept. :5, 19392,211,108 Fitzgerald Aug. 13, 1940 2,295,249 Yates Sept. B, 19422,436,451 Rosenberger Feb. 24, 1948 2,493,012 Moore et al Jan. 3, 19502,524,602 Rosenberger Oct. 3, 1950 FOREIGN PATENTS Number Country Date563,563 Great Britain Aug. 21, 1944

